1. Field of the Invention
The present invention relates to a synthesizing method for a diamond-like thin film and an apparatus for the same, and particularly, the present invention relates to a synthesizing method for a diamond-like thin film which has a comparatively wide surface area and an apparatus for the same. More particularly, it relates to a synthesizing method for a diamond-like thin film which shows good surface properties and a high crystallinity and an apparatus for the same.
2. Description of the Prior Art
There have been proposed many prior art techniques for synthesizing a diamond or a diamond-like thin film by means of a vapor-phase synthesis. However, these prior art methods have failed to synthesize a diamond-like thin film with a comparatively wide surface area. In the vapor phase synthesis, various methods have been proposed, typical ones being as follows.
a) Plasma method utilizing direct electric current, radio frequency (RF) or micro wave energy sources,
b) Ionization evaporation method utilizing ionization of gas,
c) Chemical vapor deposition method utilizing vapor phase reaction.
Almost all of these prior art techniques can not successfully synthesize a diamond-like thin film of good properties unless a substrate heated over 700.degree. C. is used. For example, in the chemical vapor deposition method, a temperature of substrate from 700.degree. to 1000.degree. C. is required, and in the RF plasma method, a temperature of substrate above 700.degree. to 1000.degree. C. is required and in the micro wave plasma method, a temperature of substrate above 700.degree. C. is required. It is well known that these methods are able to syntheze diamond-like thin films of good property. These results are disclosed in, for example, "Surface Chemistry" Vol. 5, No. 108 (1984) pp. 108-115.
However, the requirement for substrate of such high temperature disclosed in the aforementioned prior art is a severe hindrance to a trial for increasing the surface area of the substrate for a diamond-like thin film, because a substrate of a wider surface area requires more energy to heat itself above the temperature of 700.degree. C.
On the other hand, there have been proposed other prior art techniques for the vapor phase synthesis to synthesize a diamond-like thin film of good properties, utilizing a substrate at comparatively low temperatures. A substrate heated to less than 400.degree. C. for example is utilized in sputtering method, ion beam evaporating method, DC plasma method and ionization evaporating method. They are suitable for saving energy. However, these prior art methods which utilized a substrate at such a low temperature have failed to provide any adequate manufacturing process and means capable of providing a diamond-like thin film with a wider surface area yet.
The present invention relates to an improvement in the ionization evaporation method among the aforementioned prior art methods. In this method, in order to synthesize a diamond-like thin film, one or more material gases which contain carbon atoms are introduced into a vacuum chamber and are ionized by means of various ionizing means such as arc discharge between a cathode and an anode or thermionic emission between a hot cathode filament and an anode. Then, the ionized carbon-containing particles are accelerated by an electric field as a stream of ions and are deposited on a substrate to form a diamond-like thin film. The aforesaid material gas or gases may include hydrocarbon gases or gases capable of producing hydrocarbons from decomposition or from reaction. Herein, the term "hydrocarbon" means any of saturated hydrocarbons, such as methane, ethane and propane, and unsaturated hydrocarbons such as ethylene, propylene and acetylene. The material gas capable of producing hydrocarbon from decomposition, may be selected out of alcohols, such as methyl alcohol and ethyl alcohol or out of ketones such as acetone and methyl ethyl ketone. The material gas capable of producing hydrocarbon gas from reaction, may be consisted of a mixture of gas which contains hydrogen atoms such as water and of a gas which contains carbon atoms such as carbon monoxide or carbon dioxide. The material gas may contain at least one of oxygen gas, nitrogen gas and inert gas such as helium, neon and argon or the like.
The processes of synthesizing the diamond-like thin film by means of this ionization evaporation method were disclosed in the prior art such as Japanese Patent Publication for Application "Kokai" No. 174507/1983, Japanese Patent Application No. 59376/1988 and No. 59377/1988. The ionization evaporation method is well known as having a high deposition rate, and the diamond-like thin film which was made by means of the method had the features of good surface property, high degree of hardness, high conductivity and high index of refraction. Furthermore, the resulting diamond-like thin film need not any surface finishing. In this method for synthesizing a diamond-like thin film with a wider surface area, it requires filaments of a wide surface area as a hot cathode. However, filaments are generally thin and linear, and no filament has been designed to be with wide surface. Instead of the wide surface filaments, the inventors of the present invention tried to arrange uniformly a plurality of filaments on two dimensional coordinates, and to arrange one anode surrounding the whole array of filaments at a predetermined distance from the filaments. The filaments for this trial were selected from linear one or U-shaped one which has pin point top end. However, this trial did not succeed in synthesizing any diamond-like thin film of a large surface area which showed good property throughout the surface area. The trial will be explained later as the comparatives in FIGS. 6 and 7.